Turbo charged engines utilize a Charge Air Cooler (CAC) to cool compressed air from the turbocharger, before it enters the engine. Ambient air from outside the vehicle travels across the CAC to cool intake air passing through the inside of the CAC. Condensate may form in the CAC when the ambient air temperature decreases, or during humid or rainy weather conditions, where the intake air is cooled below the water dew point. When the intake air includes recirculated exhaust gasses, the condensate can become acidic and corrode the CAC housing. The corrosion can lead to leaks between the air charge, the atmosphere, and possibly the coolant in the case of water-to-air coolers. Condensate may collect at the bottom of the CAC, and then be drawn into the engine at once during acceleration (or tip-in) increasing the chance of engine misfire.
Other attempts to address condensate formation include restricting intake air travelling through the CAC or restricting ambient air flow to the CAC. One example approach is shown by Craig et al. in U.S. Pat. No. 6,408,831. Therein, the intake air temperature is controlled by an ambient air flow restriction system and an intake air flow restriction system. A controller defines the position of these restriction devices and is connected to a plurality of sensors which measure different variables such as ambient air and intake air temperatures.
However, the inventors herein have recognized potential issues with such systems. As one example, even with adjustments to the above restriction devices, condensate formation may not be sufficiently addressed. Specifically, controlling restriction devices in response to intake or ambient air temperature alone may not sufficiently control condensate formation or change charge air cooler effectiveness. Further, controlling restriction devices based on intake or ambient air temperature alone may result in increased vehicle drag and engine over temperature conditions. Maintaining temperatures at a certain level such that condensate formation is low may result in keeping the restriction devices closed or open for long periods of time. If restriction devices are closed for a prolonged period, this may result in an increase in engine temperatures over optimal levels. Conversely, if the devices are open for a prolonged period, increased air flow is received through the vehicle front end, increasing the aerodynamic drag on the vehicle.
In one example, the issues described above may be addressed by a method for controlling a vehicle electric fan, comprising: adjusting fan rotation speed or rotation direction in response to a temperature at a charge air cooler outlet. The fan may be adjusted to increase the temperature at the charge air cooler outlet (e.g., decrease rotation speed, turn rotation off, or reverse rotation direction) during a first set of conditions, and may be adjusted to decrease the temperature at the charge air cooler outlet (e.g., increase rotation speed) during a second, different, set of conditions. In this way, by controlling the temperature at the charge air cooler outlet, condensate formation may be managed, as one example.
In addition to condensate formation, an electric fan may be adjusted in response to engine cooling parameters, outside weather conditions, and non-driven vehicle conditions, such as deceleration. Adjustment of the electric fan may be coordinated with grille shutter operation in order to optimize condensate control, as well as engine cooling and fuel economy. For example, the inventors herein have identified approaches that enable the electric fan and grille shutters to still be adjusted in a way that improves fuel economy (by reducing drag) and reduces energy losses, but that also maintains engine coolant temperature control to avoid over temperature and reduces condensate formation (by maintaining CAC outlet temperature within a threshold range).
Specifically, the electric fan and grille shutters may be operated in different modes based on temperature at the CAC outlet and vehicle speed. Choice of operation mode may be further based on engine coolant temperatures and non-driven vehicle conditions. In each mode, the electric fan, grille shutters, or both the electric fan and grille shutters may be adjusted in response to the above listed parameters. In this way, the electric fan and grille shutters may be adjusted to increase or decrease CAC outlet temperature while optimizing vehicle fuel economy and energy savings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.